@UglyKidJoe
I have been using OpenHAB and MQTT for a number of years now.
The reason for using MQTT and not just a serial connection from the MySensors GW is partly the flexibility as many have stated previously here. Easy to test, using e.g. the mqtt.fx tool. If you want to know what is going on you simply connect to the MQTT stream and "snoop" on the messages.
Another reason is that I am running three geographical sites on one OH installation. OH is running on a NUC at my home. There is also an MQTT GW here. Two other My Sensors MQTT-GW are running remotely in two summer houses. The three GW connect over internet to a cloud-based MQTT broker and OH connects to the same broker. In that way I do not have to open any ports into my home network for access should I have had a local MQTT-broker at home.
Welcome to the club!
Regarding radio's: The RFM69's with a C in the type have a smaller form factor (which is pin compatible with the predecessor RFM12B). The the 'W' and "HW' versions are larger in size and have more programmable pins (which MySensors does not use) but have exactly the same functionality within MyS.
All the footprints on the boards available in OpenHardware.io are for the 'W' and 'HW' versions so I'd go with one of these.
The 'W' uses way less power than the 'HW' which would be good the for the battery life of your nodes. Sensors powered by the grid can be 'HW', but usually, in the house a 'W' delivers enough TX power to get the message across. It might be a good idea to make your gateway with a 'HW'.
Hope this gets you a bit further. Good luck and show us your results!
@tsunami My setup is max 50m radius and 433MHz standard power RFM69s so a small 1/4 wave whip works reliably even from a below ground pump chamber 10m away.
Your 915MHz at 200m SHOULD work on 1/4 wave if obstacle free line of sight, but you could try a 2.4GHz Wifi router at one location and use a mobile at the other to test if you can see the router. I can see at least 3 neighbouring routers identified on my mobile from over 40m away through masonry, 10 on the laptop, so it's a simple enough test.
If you can see the router on either, 915MHz should be rock solid with a simple whip and no need of directional antenna.